If your battery won’t charge, first look to see if the light is flashing on the charger you plug into the wall. If the light is not flashing then there may be a blown fuse in the battery charger which can be replaced. If it is not a blown fuse it may just be a defective battery or an old battery since batteries over a period of time may not be able to hold charge as well as when you first got them. So in that case I recommend buying a new charger if you can not replace the fuse on your drill.